1. Field of the Invention
The present invention relates to an electric rotating machine.
2. Description of Related Art
There is known an electric rotating machine having a structure in which the outer peripheral surface of a fitting portion of a shaft fitted into a center hole a core of a rotor is provided with axially extending convex lines formed by knurling, and the circumferential wall surface of the center hole of the core is formed with an engaging portion which engage with the convex lines to control the mutual circumferential rotation between the shaft and the core. For example, refer to Japanese Patent Application Laid-open No. 2011-239612.
Generally, the core of the rotor of a common electric rotating machine is made by laminating electromagnetic steel sheets having a high hardness. Accordingly, the core is harder than the shaft. Therefore, there is a concern that the shaft cannot be pressure-inserted into the center hole of the core with a sufficiently high insertion accuracy, and chips occur during the insertion. In this regard, the foregoing knurled shaft structure as described in the above patent document can provide a sufficiently high insertion accuracy of the shaft and lessen the stress in the circumferential direction, because there are formed relief spaces for the projections of the engaging portion of the core between each adjacent two of the convex lines of the shaft, and there are formed relief spaces for the concave lines of the shaft between each adjacent two of the projections of the engaging portion of the core.
However, the above knurled shaft structure still involves the problem that a large stress occurs in the radial direction when the shaft is pressure-inserted into the center hole of the core.